The biggest thing in my book is that when, (it's only a matter of time), you mess up the wire in a wired system your screwed. I have nothing against them and I loved mine. Worked flawlessly for years but because the wires somehow frayed or split made mine a paperweight.
If all you want to know is how far you went and how long and how fast then all you need is a basic wired, or a watch. if you want all that other stuff cadence, elevation, blah blah blah. go wireless.